Annulate lamellae are found in a variety of cell types including germ, embryonic, cancer, and tumor cells. Notwithstanding the extensive amount of morphological details reported about annulate lamellae, little is known of their functional role in cells. This organelle consists of cytomembranes interrupted at regular intervals by pores. A model cell for the study of annulate lamellae is the Necturus oocyte. In this cell, annulate lamellae originate from the nuclear envelope. Subsequently, the annulate lamellae migrate into the cytoplasm; where they form stacks, some of which are visible with the light microscope. It has been hypothesized that annulate lamellae function in the transport and storage of mRNA. To test this hypothesis, oocytes will be subjected to in situ hybridization with (3H) poly (U), a mRNA probe. The long-range objective is to gain an understanding of annulate lamellae function. The specific aims of this study are: 1) to study the origin and spatial distribution of mRNA in developing oocytes; 2) to determine if mRNA is associated with the stacks of annulate lamellae; and 3) attempt to assess the precise ultrastructural localization of mRNA, particularly in reference to annulate lamellae.